VLSI Design and Embedded Systems Group
Introduction
The current research activities of the VLSI Design and Embedded Systems (VDES) group can be divided in four streams as described below.
Minituarisation of the small satellite platform:
The continuous evolution of communication satellite platforms demands the use of modern approaches to system design. The up-and-coming new wave of smaller satellites currently in the pipeline are nano-satellites, ranging from 10 kilograms down to 1 kilogram, and pico-satellites that weigh in at less than 1 kilogram. The smallest category envisioned is the femto-satellite at less than one-tenth of a kilogram, a satellite that would handle very simple missions and would be implemented on a single chip, this is why they are also called satellites-on-a-chip.
Reconfigurable system-on-a-chip platform for satellite on-board computing
Small satellites aim to achieve low-cost, fast access to space and this is normally supported by the use of off-the-shelf components (COTS) and development tools. The advances in micro and nano technology, which have already brought to life remarkable new products and capabilities in terrestrial systems, are bound to change the way in which satellite on-board computing and electronics are designed. Computing has always played an important role in on-board data processing and control. Historically on-board computing has been represented mainly by the on-board computer (OBC) as the kernel of the On-Board Data Handling (OBDH) system, which is central to the overall satellite design and its operations. The OBDH system is an integral part of the satellite platform and in many missions extends to comprise elements of payload electronics. Nowadays, a computer controls almost any single on-board sub-system and the on-board computing system is represented by a number of processors connected by an on-board data network. The increased number of computing elements on-board is possible due to the emergence of advanced miniaturization technologies, which have given birth to multi-million system-on-a-chip (SoC) processor designs. This trend is going to be continued further and it is expected that in the near future all the electronics of a fully functional satellite will be condensed into one multi-chip module.
This project is aimed at application of advanced technologies to on-board computing. A generic single-chip computing platform for use on-board small spacecraft, which can be reconfigured remotely from the ground station, is proposed. The platform features a highly modular structure, such that it can be quickly and easily customised to produce specific-purpose controllers for data processing, communication and control of different spacecraft subsystems and payload blocks. The platform is targeted at the QPro radiation tolerant family of Xilinx Virtex FPGAs. It is composed of reusable soft IP cores and is centred on the LEON microprocessor core and the AMBA on-chip bus. Two schemes for on-board run-time partial reconfiguration are specified, which will facilitate adding and updating of peripheral cores remotely (in space) while the rest of the OBC is operational. In addition, a 3-tier client-server remote configuration scheme with the Common Object Request Broker Architecture (CORBA) is proposed to support the run-time reconfiguration of the on-board platform in a LEO constellation of small satellites over TCP/IP.
Satellite-on-a-chip design
Over the past 20 years there has been a gradual return to missions enabled by smaller satellites that are becoming increasingly capable and cost-effective. The "satellite-on-a-chip" concept can be viewed as the ultimate miniaturization goal of the small satellite platform. This study is focused on the feasibility of monolithic integration of a payload with supporting subsystems all on a commercially available bulk-silicon foundry process. The initial literature review and theoretical paper design reveals that it is not only possible, but will soon be a reality. SpaceChip will make possible a vast array of proposed missions that rely on distributed simultaneous multipoint sensing using thousands of satellite-on-a-chip nodes.
Inter-node networking and distributed computing in satellite constellations:
Distributed computing in satellite constellations
There is a continuing trend in the space community to reduce costs involved in space missions. Miniaturization has been the primary method that was deployed for reducing space mission costs. This is now changing, due to the recent advancements in technology that enable advanced mission architectures namely, distributed spacecraft missions. Several spacecraft flying in close formations would collaboratively achieve the mission aims at lower costs and with enhanced reliability compared to larger single platform missions. While research in the area of formation flying is quite active in technologies that are key to the success of such missions, such as the development of efficient control algorithms, reliable inter-satellite links and precise navigational techniques, other areas are dealt with to a much lesser extent. In this research work we exploit the utilisation of the spatially distributed nature of formation flying missions in forming a distributed computing system over the inter-satellite network.
Intersatellite links using the wireless protocol IEEE 802.11 and SpaceWire (IEEE-1355)
Incorporating IP-compliant technologies could potentially allow seamless interoperability and connectivity between all subsystems in a single spacecraft as well as between spacecraft in a constellation or formation. An inter-satellite link (ISL) network distribution system based on IP-compliant wired and wireless protocols and implemented using commercial-off-the-shelf (COTS) components will contribute significantly to the implementation of Internet in the sky. In this research we will investigate the impact of inter-satellite links on the performance of the IEEE 802.11 standard for LEO satellites in polar orbit. The performance of the protocol will be optimised to account for the complexity of LEO satellite networks. The IEEE 802.11 physical and medium access control (MAC) layers will be optimised for ISL ranges without any modification to the standard by re-defining the inter-frame signals and using antenna null steering. Recently, there has been increasing interest in integrating both the physical and MAC schemes for use in ad hoc networks where nodes are equipped with smart agile directional antennas, however space applications have not been addressed. Our proposed IEEE 802.11 architecture with the integration of smart antennas will allow the seamless connectivity between modules and spacecraft in a changing LEO topology. The use of high-gain and agile antennas and the integration of a MAC-layer protocol will enable the finding and tracking-over-time of every in-range neighbouring satellite with minimal interference. This research is also aimed at building an IEEE 802.11/SpaceWire communication platform that will achieve a fault tolerant connectivity between all subsystems in a single spacecraft as well as between spacecraft in a constellation or formation. This will give less redundancy and more flexibility, which is of particular benefit to smaller spacecraft that are constrained by mass and volume.
ESPACENET: Intelligent sensor networks for space applications
This project is funded by the EPSRC and is undertaken in collaboration with the Universities of Edinbugh and Kent, JPL/NASA, SSTL, Epson and Gateway. It targets the development of flexible and intelligent embedded networked systems for aerospace applications. The space application domain presents unique challenges to embedded electronics design. Not only designers should deal with the harmful effects inherent to the space environment, not only should they design complex optomechatronic systems with minimum power budget, but they should also be able to provide for the fact that equipment is unavailable for physical upgrade or repair after it is launched in space. At the same time the significance of the space domain is growing due to the environmental problems on Earth that require detailed and sophisticated monitoring from space taking into account Earth's interaction with other celestial bodies.
There are several opportunities for applying networked PicoNodes to this application domain. First of all, there is a pressing need for condition-based maintenance and repair on-board aerospace vehicles where networked wireless sensors can take on tasks of remote monitoring, diagnostics and self-repair, ensuring correct operation, longer life and higher quality of service. Secondly, the proposed PicoNodes concept could directly be employed in the construction of networked miniaturised pico-satellite nodes based on wireless sensors, which could be used as co-orbiting assistants/inspectors of larger mother ships such as large satellites, the space shuttle or the international space station. Thirdly, future spacecraft are envisioned as highly miniaturized autonomous, intelligent and distributed space micro-systems. Therefore constellations of pico-satellites could serve as embodiment of that vision offering new space architectures that are based on large (hundreds-to-thousands) numbers of individual spacecraft. Pico-satellite constellations could be used to form "virtual satellite" missions, which could give rise to a new distributed approach to building large spacecraft that is much more cost-effective and flexible.
Pico-satellite constellations could provide continuous Earth coverage for communications or Earth imaging at low cost. They can also provide widely-dispersed monitoring of the space environment, e.g. magnetic field measurements. Finally, multiple spacecraft can operate together to simulate large (greater than a kilometer) apertures through coherent beam combining to create highly-directional antenna gain patterns for radio astronomy, high bandwidth communications, or multi-static radar. Pico-satellite constellations can also play a role in interplanetary applications. Global constellations can be placed around the Moon, Mars and other planets or asteroids to provide continuous communications for multiple low-powered surface vehicles, timing signals for a planetary positioning system, or medium-resolution planetary imaging with short revisit times located at various altitudes from earth for tasks such as monitoring environmental conditions around planet Earth or other planets.
Although targeting aerospace, the results of this work will lead to new technological solutions, which will be beneficial not only to the aerospace domain but also to various Earth-bound applications. These include environmental and medical diagnostics, which involve insertion of sensor nodes into relatively hostile environments.
Intelligent processing of multispectral images on-board satellites:
Automatic registration and change detection
Currently degree of automation in image processing on-board remote sensing satellites is low. Most of the remote sensing satellites operate 'store-and-forward' mechanism. In this concept, after the on-board sensors scan a scene it is stored and later it is transmitted to the ground station. However, the increased technical capabilities of today's satellites and the advances in technology provide the necessary infrastructure for implementing on-board intelligence. There is a need for hardware implementation of change detection on-board in order to increase the automation capabilities on-board the satellites. The objective of this project is to investigate the feasibility of implementing such intelligence system on-board small satellites that can perform critical image processing tasks such as image registration, change detection and image compression. The current stage of the research is concerned with the development of an Automatic Change Detection System (ACDS), as shown in Figure 1, and to evaluate its performance against state-of-the-art on-board computing systems of small satellites. Currently the evaluation is based on the small satellite platform of the Disaster Monitoring Constellation (DMC) developed by SSTL , e.g. UKDMC, AlSAT-1 and the recently launched Beijing-1.
Compression
Earth Observation Satellites require transmission to ground of an extensive amount of imaging data. The data transmission capacity of onboard equipment these days is reaching up to several times as large as the down link circuit capacity provided by present satellites. High-speed data compression is required in order to transmit the image data to ground stations in real-time. Data compression is seen as a solution to the "Bandwidth Versus Data Volume" dilemma of modern spacecraft. Compression reduces the amount of data to be sent whilst preserving its content, allowing a lower bit-rate link to be used or more data to be sent over the same link.
We have investigated existing image compression methods and have developed fault-tolerant software suitable for use on-board a DMC satellite. Five different image compression programs capable of lossless, near lossless and loss afflicted compression were used in this study. A fault-tolerant compression scheme was proposed and implemented, which employs a fine-grained tiling mechanism. An improved Neural Network-based data compression method was also developed. The investigated compression methods were compared in terms of error resilience, compression ratio and execution time. A good illustration of the effectiveness of the fault-tolerant scheme is the Neural Network-based algorithm, which achieved 100% useful recovery although originally the entire file content became corrupted in the event of a single bit-flip in the compressed file. Furthermore, additional pre-processing stages were specified and developed, which improve the image compression ratio.
Hardware acceleration of computationally intensive algorithms:
Encryption
The unfortunate events of 11th September 2001 have raised awareness of the security threats posed by the unauthorized use of public assets. Satellites and the data that they generate are no exception. Although there are many encryption products and algorithms, the use of these products and algorithms on-board satellites and satellite networks has been over looked until recently. This is partly due to the impression that satellites are very complex and very far to the intruders to access its sensitive data. But this is no longer true, especially after the cases where it has been proved that intrusion into satellite data is not an impossible task. The demand to protect the sensitive and valuable data transmitted from satellites to ground is increasing day by day and hence the need to use encryption on-board.
At present, very few satellites are using on-board encryption to protect the data transmitted to the ground station. The encryption algorithms used in present satellite missions are typically proprietary algorithms or outdated algorithms like DES rather than using the latest encryption standards. The Rijndael algorithm approved as the Advanced Encryption Standard (AES) by the US National Institute of Standards and Technology (NIST) in October 2000 is being adopted by many organizations across the world. It is used across a wide range of platforms ranging from smart cards to big servers because of its simplicity, flexibility, easiness of implementation and high throughput. Therefore, the AES is well suited for resource constraint platforms like on-board satellites. The Consultative Committee for Space Data Systems (CCSDS) is considering recommending AES as the standard encryption algorithm for use on satellites.
The current stage of the research is aimed at an optimal and reliable (fault-tolerant) implementation of the AES algorithm such that it satisfies on-board resource constraints in terms of power, area and speed.
